Every 12JP4 I've had the misfortune of coming across has had this burn to some degree or another, this one is the worst.

It also had the worst emissions so probably a high hour tube, I cleaned it with the Beltron to get some brightness out of it, it really just made the spot look worse.
It's Green because it's a Hoffman.

A bit off topic, but...
...there is some strange bug in my brain that always causes me to, whenever I look quickly at a picture of a GE 801 TV, I always see it as having a big ion burn on the screen on the left.

A bit off topic, but...
...there is some strange bug in my brain that always causes me to, whenever I look quickly at a picture of a GE 801 TV, I always see it as having a big ion burn on the screen on the left.

TV monster is bored. TV monster wonders what other living rooms are on. :D
http://www.videokarma.org/attachment.php?attachmentid=194395&d=1491268752

M3-SRT8

04-05-2017, 12:30 PM

Ion burn seems to be a recurring problem with DuMonts and Andreas.

For me, anyways.:smoke:

benman94

04-05-2017, 12:52 PM

Ion burn is just a consequence of not having an ion trap or an aluminum backed screen. The ions are too heavy to be deflected along with the electrons, so you get a big nasty spot on any trap-less, non-aluminized magnetically deflected CRT. All 12JP4, 15AP4, 20BP4, 12AP4, and 9AP4s will burn sooner or later.

Kamakiri

04-05-2017, 02:02 PM

I seem to remember reading about an "X" shaped ion burn in a very good book by Robert G. Middleton, saying that it would happen on rectangular screen sets. I've never seen one nor ever heard anyone mention one before. Has anyone seen one?

Electronic M

04-05-2017, 02:19 PM

I seem to remember reading about an "X" shaped ion burn in a very good book by Robert G. Middleton, saying that it would happen on rectangular screen sets. I've never seen one nor ever heard anyone mention one before. Has anyone seen one?
Pretty, sure whoever you heard that from must have been mistaken. First off as Ben already said ions can't be deflected (too much mass), so the burn is limited by the scatter pattern of the electron gun. By the time rectangular CRTs were in consumer sets ion traps were standard, and aluminization was catching on...

Kamakiri

04-05-2017, 02:27 PM

Nope, nope.....had the book (sort of) handy. See?

benman94

04-05-2017, 02:27 PM

Well, you can deflect an ion, just do it electrostatically. Charge predominates, and since an ion would have a magnitude of charge greater than or equal to the elementary charge, they'll zip right along with the electrons. This is why a great number of 7JP4s show decent emissions but look like garbage; they have a "whole-screen" ion burn.

Aluminization was becoming standard, the ion trap had been a standard for many years. In addition, I can't think of any mechanism that would lead to an X shape, aside from some element of the gun acting as a sort of crude, unwanted collimator for the ion beam.

That page from the book is puzzling.

Edit: If it is more likely on a rectangular tube, then it likely has something to do with electrostatic focusing or self focusing elements. Weren't the vast majority of the 1946 to circa 1950 round B/W tubes magnetic focus?

Eric H

04-05-2017, 02:58 PM

It's strange that Dumont, the Cadillac of Televisions, went with such an oddball CRT.

Not only is it not Aluminized, it's also made of thin glass and has a bulbous pre war shape, it's only advantages I can see is it's lighter, and they didn't seem too concerned about weight.

Others like Zenith and GE were using Aluminized tubes as least as far back as 1948. I wonder who had the Patent on that?

Electronic M

04-05-2017, 03:45 PM

It's strange that Dumont, the Cadillac of Televisions, went with such an oddball CRT.

Not only is it not Aluminized, it's also made of thin glass and has a bulbous pre war shape, it's only advantages I can see is it's lighter, and they didn't seem too concerned about weight.

Others like Zenith and GE were using Aluminized tubes as least as far back as 1948. I wonder who had the Patent on that?

It's an oddball because Dumont made their own CRTs. My guess is Dumont was still using their pre-WWII (pyrex) tooling and methods for a while post war.

IIRC Dumont's CRT tech was state of the art pre-war (they had the biggest domestic production CRT 14"). Post war I think they were the first with a 20" CRT so they still lead, but as others made advances they were slow to latch on and mix in other's tech.

benman94

04-05-2017, 03:53 PM

DuMont was building radar and CRO tubes for the war effort. Most of these tubes are just P4 versions of those same tubes. I have a collection of in-house datasheets with developmental numbers from '44 or '45. It's easy to match the 12JP4, 15AP4, and 20BP4 to the developmental types. They also pioneered the lackluster 7EP4 (rapidly displaced by the 7GP4/7JP4). Some of the developmental types died off however. It's interesting reading.

Notimetolooz

04-05-2017, 07:19 PM

I seem to remember reading about an "X" shaped ion burn in a very good book by Robert G. Middleton, saying that it would happen on rectangular screen sets. I've never seen one nor ever heard anyone mention one before. Has anyone seen one?

I must have had that book at one time. The page looks familiar and I too remember about "X" ion burns. I think it is because the ions are deflected some and they kind of lag behind the electron deflection, the sweep being rectangular. Maybe the rectangular tubes tended to have stronger fields since the deflection angles were greater because of the more recent design that the round.

benman94

04-05-2017, 08:05 PM

No ions are being deflected by an appreciable amount in an electromagnetic deflection tube, period, unless an electrostatic focusing element is screwing with them.

A proton is about 1836 times as massive as an electron. (An electron is about 0.511 MeV over the speed of light squared, a proton is about 938 MeV over the speed of light squared, a neutron is about 939 MeV over the speed of light squared.)

I'm not sure which ions you would expect to find in a CRT, but let's assume it's something relatively light, comparable to an alpha particle at a mass of 3.727 GeV per speed of light squared. Now we're talking about objects on the order of 7294 times as massive as the lowly electron. Electromagnetic deflection from a TV yoke isn't going to do jack to a proton or neutron, and certainly not something similar in rest mass to an alpha particle.

Eric H

04-05-2017, 08:39 PM

I've heard the theory about Ions ruining 7JP4's before, maybe theoretically possible but I have my doubts that it happens in practice.

I've had plenty of tired 7JP4's, but they pretty much were all bad the same way, very dim and going negative at higher brightness.

Maybe I've just never come across one with a burned screen that still had good emissions since high hours and burned screen would go hand in hand.

Still I would expect an Ion burned tube to be burned only where the image was, in other words if you increased the scanning height or width it should be okay at the edges.

I have seen one 10BP4 (or maybe it was a 12LP4) where you could tell where it had been scanned most of it's life, if you rotated the yoke you could tell the difference in the color of the phosphor. I'm guessing that was simply worn phosphors and not Ion burn.

benman94

04-05-2017, 08:49 PM

Ion bombardment definitely does do damage to the screen. Whether you notice it is a different story. Since the ions are deflected as well, the damage that would normally be a big nasty dot in the center of the screen is spread out over the whole screen. To get adequate brightness out of a damaged phosphor back you crank up the controls. Of course the cathode is wearing simultaneously as well, so eventually, the pairing of a damaged phosphor and a weak cathode gives the tell-tale shimmering, and eventually negative, picture. If you could isolate the effect of the ion bombardment though, let's say with some super long lasting cathode material, you would see detriment to the screen.

You're also correct in saying that on a 7JP4 you would expect to see the ion damage in the region of the previously scanned raster.

On the 10BP4 or 12LP4, it was assuredly damage from the electrons themselves; the ions were shot off into the wall of the neck. Remember that an electron in the region of ~2 keV in a lowly 7 inch Transvision to ~75 keV in some projection sets can and will do incremental damage to the phosphor. Ever seen a burned 5TP4? That was done by a beam of electrons at 25-27 keV over some extended period of time.

Kevin Kuehn

04-05-2017, 09:08 PM

You don't suppose that the anode voltage in conjunction with the shape of the CRT envelope has some influence on the ion defection pattern? There's got to be some electrostatic effect involved between the anode and ions.

benman94

04-05-2017, 09:14 PM

It's possible, but then why the corners? The whole bulb needs dag, inside and out, and all of the exterior dag should be at ground, and the interior at whatever your ultor voltage is, say 20 kV for a big glass 27 inch rectagular tube.

There's only one solution: when CRT rebuilding gets off the ground, have Nick rebuild an un-aluminized 17 incher with a straight magnetic focus gun, and run that S.O.B into the ground.
Then rebuild a second, identical bulb, with a straight electrostatic focusing gun. Run it into the ground.

I strongly suspect the 'static focus gun will show the X and the magnetic gun just a spot...

The difference in mass/charge ratio between the electron amd any ion is just too great for a magnetic explanation to make sense IMO.

jr_tech

04-05-2017, 09:14 PM

You don't suppose that the anode voltage in conjunction with the shape of the CRT envelope has some influence on the ion defection pattern? There's got to be some electrostatic effect involved between the anode and ions.

Have we considered ion production in the space between the deflection yoke and the screen? For sure, there were a number of un-aluminized rectangular crts produced in the 50s that had an ion trap, but the screen possibly could have been bombarded by ions produced past the electron gun. :scratch2:

jr

benman94

04-05-2017, 09:19 PM

Have we considered ion production in the space between the deflection yoke and the screen?

jr

What's going to produce the ions? Are we assuming that the electron beam interacts with residual gas, and ionizes it post-deflection? That's an interesting angle, but I don't see how the X pattern results...

benman94

04-05-2017, 09:29 PM

All of the ions in the tube would be produced by residual gas interacting with the electron beam, so I'm guessing helium and hydrogen nuclei are the most likely ions encountered. They're the lightest gases; most likely to "sneak" in through a leak. There might be some diatomic oxygen, diatomic nitrogen, and a bit of carbon dioxide left in the tube as well that could cause issues.

jr_tech

04-05-2017, 09:39 PM

What's going to produce the ions? Are we assuming that the electron beam interacts with residual gas, and ionozes it post-deflection? That's an interesting angle, but I don't see how the X pattern results...
Yes, but I don't have a clue as to how the x shape might be produced.

jr

Perhaps a bit of argon, as well?

.

Kevin Kuehn

04-05-2017, 10:05 PM

I was thinking the geometry of the envelope could have some influence on the distributed static field. A round envelope would seem to have the most even distribution.

bandersen

04-05-2017, 10:30 PM

I have a non-aluminized rectangular CRT that was rebuilt with a straight gun. It has the usual round ion burn.

There were also straight guns with diagonal-cut(slash field) type of ion traps, so you can't assume they were not ion trap guns strictly by the lack of bend in the gun. But that one Bob has apparently was not rebuilt correctly.

Phil Nelson

04-05-2017, 11:25 PM

I have seen one 10BP4 (or maybe it was a 12LP4) where you could tell where it had been scanned most of it's life, if you rotated the yoke you could tell the difference in the color of the phosphor. I'm guessing that was simply worn phosphors and not Ion burn.The 10BP4 in my RCA T-100 looked like that. The scanned area was visibly browner (or less blue) than the portion that was never scanned. Looked weird until I put the set back together and rotated the CRT to match the brown area to the CRT mask. In the second photo, I taped the CRT to mark the edges of those zones, which were more obvious to the eye than in photos.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

http://antiqueradio.org/art/RCAT-100PurpleCRT01.jpg

http://antiqueradio.org/art/RCAT-100PurpleCRT04.jpg

bandersen

04-05-2017, 11:45 PM

Bob,
The rebuilt rectangular tube is magnetic focus, no?

Ah, electrostatic. I hadn't thought about that. I guess that would account for the small spot?

benman94

04-06-2017, 08:49 AM

Ah, electrostatic. I hadn't thought about that. I guess that would account for the small spot?

Or if the tube hasn't been used much, you should expect an incredibly small spot in the center.

My hunch right now is that the ions are scattering off some element of a particular gun type, and it's creating the characteristic X pattern shown in that manual. I'm not necessarily talking about 'static vs magnetic focus here, but rather some difference in physical construction. I've seen 10BP4s with very different looking guns that functioned identically. This gun type probably became more popular around the advent of the rectangular tube. Note that the page from the book doesn't exclude the possibility of a round tube developing the X pattern burn, it only says it's much more likely to be seen on a rectangular tube.

I'm not buying into a mis-adjusted ion trap hypothesis. A mis-adjusted trap would only allow the electron beam to overheat an element of a gun, perhaps burning a hole in it. I doubt very much that any trap magnet can produce the field strength necessary to redirect the ions toward the screen.

Notimetolooz

04-06-2017, 01:01 PM

I did occur to me that the ions would be hitting the wall in a bent gun tube and since the ion trap magnet isn't strong enough to effect the ions much, they would never reach the screen. Even if the trap was mis-adjusted. I remember seeing a picture. maybe in that same book, of a gun element with a notch in the side of the aperture, produced by electron bombardment from a mis-adjusted trap.

jr_tech

04-06-2017, 01:28 PM

Other than a picture (or artist conception) in one or several tv repair books that many of us have seen, has anybody here actually seen an "X" shaped ion burn in real life? Under what conditions?

jr

benman94

04-06-2017, 01:53 PM

Is it possible that the phosphor damage in an X shape is really NOT an ion burn? I can't think of another reasonable explanation, but it wouldn't be the first time one of those repair books misattributed a symptom to the incorrect cause.

Gleb

04-06-2017, 05:14 PM

I have a CRT that had worked for a long time with a misaligned ion trap magnet. The result is a sickle-shaped ion burn:

http://i042.radikal.ru/1704/51/5a923caeaaa6.jpg

Although, it isn't very noticeable on a real picture:

http://s001.radikal.ru/i193/1704/5e/a08b00f80d0e.jpg

The bad thing is that the misdirected electron beam may bombard and overheat an element of the gun, causing release of gases from its surface and hurting the vacuum, thus even more ions are produced

Kevin Kuehn

04-06-2017, 05:31 PM

Although, it isn't very noticeable on a real picture:
http://s001.radikal.ru/i193/1704/5e/a08b00f80d0e.jpg

Nope I can't see any ion burn in that picture. :D

Zenith26kc20

04-06-2017, 10:34 PM

This may answer why 7JP4 tubes were not rebuilt in the past (from what I have learned). If the phosphor is dead, it may be too costly to recoat on what, at the time was becoming an obsolete tube.
I guess I'm lucky with my 10 and 12 inch tubes. I see no ion burn on any, even the really high hour.
Would a double ion trap vs a single make a burn difference?

Gleb

04-07-2017, 01:51 AM

I guess I'm lucky with my 10 and 12 inch tubes

Yes you are, because the only thing responsible for ions is the quality and depth of the vacuum inside a CRT. That's why some straight-gun CRTs work for decades with no ion burn, while some others catch a horrible one in a year or two.
A fellow CRT rebuilder says that their shop has a very positive experience of rebuilding tubes with neither ion trap nor aluminizing. They use some modern, "very advanced" vacuum pumps, and ovenize CRTs very hard before evacuating.

jr_tech

04-07-2017, 01:41 PM

A fellow CRT rebuilder says that their shop has a very positive experience of rebuilding tubes with neither ion trap nor aluminizing. They use some modern, "very advanced" vacuum pumps, and ovenize CRTs very hard before evacuating.

CRT rebuilder?? Wow! Do they do any rebuilds for customers outside of the country?

jr

benman94

04-07-2017, 01:47 PM

I would be very leary of a Russian rebuilder. Look at the "quality" of Russian small signal tubes...

Gleb

04-07-2017, 02:13 PM

Do they do any rebuilds for customers outside of the country?

I think they could do, but safe shipping would be the main problem...

Look at the "quality" of Russian small signal tubes...

And what's wrong with them? :scratch2: I've never bumped into any problems with Russian tubes, at least with vintage ones.
Anyway, they do provide a nice warranty, as well as use modern brand-new cathodes with 10000-hour lifetime.

P.S. If you'd like to discuss the quality, let's get started with a random example: 2A3 RCA vs 2S4S Svetlana (https://www.dropbox.com/sh/7npppn43d1r4q10/AADd-yUgzz5KP4JQpoajDf2ya?dl=0)

Tubejunke

04-11-2017, 03:48 AM

I did occur to me that the ions would be hitting the wall in a bent gun tube and since the ion trap magnet isn't strong enough to effect the ions much, they would never reach the screen. Even if the trap was mis-adjusted. I remember seeing a picture. maybe in that same book, of a gun element with a notch in the side of the aperture, produced by electron bombardment from a mis-adjusted trap.

Hence the reason why the traps used to be called beam benders by techs or engineers. This is a good thread, but I'm still left with a question that's been in my mind for many years, but never really needed answering as I never burned a tube. The procedure I have always used (I forget now where I learned it) is to set brightness to a mid level with the magnet in approximately the correct position (over the split/gap in the gun) and rotate for max brightness. Then move slightly back and forth again for max brightness. Sometimes corner shadows require retouching of the magnet. I assume that maladjustments that produce burn must be if the magnet is adjusted for anything but max brightness. I never have taken a chance on that and always work fast when setting one.

Here's another interesting topic that I don't believe is covered here. What about the double ion trap magnets. A crt such as a 10BP4 calls for one. I have an RCA 8T 243 (that I am trying to get rid of) that I got with a 10BP4 and it had a single trap. It did produce a raster, but reading data on the set and the tube told me that it needed this double magnet, so I found one thanks to the Internet and possibly this site. Before the WWW, it would be almost impossible to find such an item. Anyway, it's still there and I never finished the set's slated restoration. I think I will snag the trap when I find a home for it. I will of course inform the new owner who will still be getting a heck of a deal.:thmbsp: Point being, I never knew and still don't know what the double magnet does that a single doesn't and why some tubes call for one and not the other specifically. I bet there are a bunch of BP4 owners here that are running on a single trap with no problem.

Notimetolooz

04-11-2017, 11:14 AM

This is an interesting thread, I hadn't thought much about it.
Whether the gun needs a double magnet probably just depends on the gun design. Its also possible the if the tube is rebuilt it might not have the original gun design. Seems like there were many types of gun designs. The people that designed the guns must have understood how the ion traps worked, some of that info must have been lost.
Probably a lot of experimentation. 'Beam bender' does seem a more accurate term.
Whether the 'burn' on a crt is made by ions and just were they come from to do the damage is a good question.

benman94

04-11-2017, 12:56 PM

I think they could do, but safe shipping would be the main problem...

And what's wrong with them? :scratch2: I've never bumped into any problems with Russian tubes, at least with vintage ones.
Anyway, they do provide a nice warranty, as well as use modern brand-new cathodes with 10000-hour lifetime.

P.S. If you'd like to discuss the quality, let's get started with a random example: 2A3 RCA vs 2S4S Svetlana (https://www.dropbox.com/sh/7npppn43d1r4q10/AADd-yUgzz5KP4JQpoajDf2ya?dl=0)
I've had issues with Russian tubes, and they have a very low reputation among most audiophiles and antique radio restorers. Even the terrible Chinese tubes seem to be better. I'll wait for rebuilding to get off the ground at the ETF...

bandersen

04-11-2017, 01:12 PM

Yes, it depends on the gun design. The two basic types and bent gun and slant cut. As near as I can make out, the bent gun uses a single magnet and the slant cut uses a dual trap.

I agree with what notimetolooz posted earlier. You're not going to cause ion burn by a misaligned trap but you can damage the gun elements with the electron beam.

Here's a diagram of how the double magnet type works.
https://c1.staticflickr.com/3/2808/33978096805_1369046747_o.png (https://flic.kr/p/TLwCpg)

Gleb

04-11-2017, 01:49 PM

The procedure I have always used is to set brightness to a mid level with the magnet in approximately the correct position (over the split/gap in the gun) and rotate for max brightness. Then move slightly back and forth again for max brightness

That works properly only if the magnet keeps its initial power. Howewer, Al-Ni-Co magnets are often degaussed from aging. A degaussed magnet seems to behave properly while aligning, i.e. it still provides some "max brightness" position, but this does not mean that the whole electron beam reaches the screen.

You're not going to cause ion burn by a misaligned trap but you can damage the gun elements with the electron beam

I have at least one reverse example with a bent-gun picture tube, but it could happen from a degaussed magnet as well.

I've had issues with Russian tubes, and they have a very low reputation among most audiophiles and antique radio restorers

They just have to be well-chosen. There are some top-grade ones (Svetlana, MELZ - just look at the pictures I attached to the previous post), some normal "workhorses", and, as always, some crappy crap hurting the whole reputation. I'm guessing that I should write some sort of choose guide here.

Zenith26kc20

04-11-2017, 02:11 PM

I have always tried to keep the ion trap with the set it came with. My highest hour is a Motorola with a 12lp4 (can't remember the chassis but I think it is either made in 1949 or 1950. Original tube as far as I can see. Good and clear, no burn and many(!) run hours! My TS-4J takes a bit to get bright but looks good after about 10 minutes.
As for Russian tubes, my worst fire breather is a Audio Research D-150 (1976). I use Svetlana 6550B types in regulator and output. This critter will kill a set of GE welded plates in about 2000 hours. I've had the Svetlana going on 3000 hours (close to needing a change according to ARC) but no sparks/blown $11.00 dollar fuses in a long time. I have heard the "C" types are better but I'll wait till it no longer meets specs to change anything. I also have the Svet "B" types in my D-115. The D-115 laughs at Chinese tubes! Then eats them!

Tubejunke

04-12-2017, 02:35 AM

LOL, we forgot to talk about the sets that left a single spot at dead center of the crt for a few minutes after the set was turned off. I have heard that those crts can show a burn, but I'm sure it would be after many years of service. And the only sets I've ever seen that do this are 60s sets which means that it has nothing to do with ion traps as they were gone the way of the Edsel by that point in time.

Point being I guess that not just ions can destroy the phosphor of a crt. Any type of concentration of the electron beam over a long duration will burn into the tube. That's why we turn down the brightness if working with a set that has lost vertical or horizontal deflection. I made the mistake of not doing that years ago and ended up with a perfectly performing set with a beautiful line burned into the crt.

Electronic M

04-12-2017, 09:43 AM

LOL, we forgot to talk about the sets that left a single spot at dead center of the crt for a few minutes after the set was turned off. I have heard that those crts can show a burn, but I'm sure it would be after many years of service. And the only sets I've ever seen that do this are 60s sets which means that it has nothing to do with ion traps as they were gone the way of the Edsel by that point in time.

Point being I guess that not just ions can destroy the phosphor of a crt. Any type of concentration of the electron beam over a long duration will burn into the tube. That's why we turn down the brightness if working with a set that has lost vertical or horizontal deflection. I made the mistake of not doing that years ago and ended up with a perfectly performing set with a beautiful line burned into the crt.

I had an aluminized CRT in a 59' Zenith with the power-off spot burn hole in the phosphor...I found a better tube in the last year and dumped the working one with the spot off on someone.

Tubejunke

04-13-2017, 12:42 AM

I had an aluminized CRT in a 59' Zenith with the power-off spot burn hole in the phosphor...I found a better tube in the last year and dumped the working one with the spot off on someone.

I had a really nice 59 Zenith Space Command floor model with the 24" tube. I tried and tried to find a home for it. Never could; not even free. I wound up saving the chassis and the remote stuff and busting up the rest. I hate is so bad when that has to happen. It would have made someone a real nice daily watcher as there was almost no hours of use on it. I say that as the chassis was only lightly dusted with all factory Zenith tubes. The crt was super bright and crisp. Man, I better shut up or people are going to want to kick my butt! LOL. It's what happens when ya bring a woman into the home. Now shes gone and it's gone, but there's now room for me to work on my Zenith "roundie"!!!!

If ya still have the thing, I have all sorts of parts.

Electronic M

04-13-2017, 09:19 AM

I had a really nice 59 Zenith Space Command floor model with the 24" tube. I tried and tried to find a home for it. Never could; not even free. I wound up saving the chassis and the remote stuff and busting up the rest. I hate is so bad when that has to happen. It would have made someone a real nice daily watcher as there was almost no hours of use on it. I say that as the chassis was only lightly dusted with all factory Zenith tubes. The crt was super bright and crisp. Man, I better shut up or people are going to want to kick my butt! LOL. It's what happens when ya bring a woman into the home. Now shes gone and it's gone, but there's now room for me to work on my Zenith "roundie"!!!!

If ya still have the thing, I have all sorts of parts.

I've been thinking about buying the tuner and space command hardware off of you to upgrade mine to space command (it has the bezel microphone and chassis shelf space for space command but was not equipped) for a few years. It might finally be time for me to pull the trigger after the ETF.

nasadowsk

04-13-2017, 07:01 PM

I had an aluminized CRT in a 59' Zenith with the power-off spot burn hole in the phosphor...I found a better tube in the last year and dumped the working one with the spot off on someone.

Had one of those years ago. Mine was a vertical chassis console. I hate vertical chassis sets :/

benman94

04-20-2017, 05:57 PM

"Ion burns" on tubes without straight guns are not in fact "ion burns" in the sense some people still seem to believe:

http://www.videokarma.org/showpost.php?p=3182920&postcount=8

http://antiqueradios.com/forums/viewtopic.php?f=3&t=316871&start=40

Thank you Kevin!

Eric H

04-20-2017, 09:26 PM

"Ion burns" on tubes without straight guns are not in fact "ion burns" in the sense some people still seem to believe:

Well that's interesting reading.
In that case the burn on my 12JP4 is an Ion burn because it has a straight gun, but the spot on the 8AP4 would be from vaporized metal from the gun.

I once had a 17" bent gun CRT from a Setchell Carlson (This one in fact http://www.vintagetvsets.com/setchell.htm) that had several flea bites on the inside of the screen that looked like micrometeorites had stuck the phosphor and blasted it off.

These weren't large fuzzy spots but more like how a windshield gets pitted when a small stone hits it, only the Phosphor was affected though, not the glass itself.

Possibly the beam had hit the screen when there was no sweep but these were off to the the side, not dead center.

benman94

04-21-2017, 12:28 PM

Also note that WeekendHacker's analysis of ion deflection/ion burn size is incorrect. An ion is NOT deflected by 10% of the deflection angle the electron beam undergoes. He's completely missing the fact that the ions in a magnetic focus tube are NOT being focused before undergoing the minute degree of deflection they experience. Well, they are being focused, but again, the magnetic field has such a minute effect on the ions, that they are essentially unfocused in comparison with the electron beam. If you had a 'static focus tube like a 12AP4 or a 9AP4, you should see a MUCH smaller ion burn because the ions are focused along with the electron beam, and then deflected to a marginal degree by the magnetic field. The ion burn on a 12JP4 is comparatively large because the ions are essentially unfocused. The large burn is NOT a product of deflection; his assertion that the ions are undergoing 10% of the deflection experienced by an electron is absolute hogwash.

Does anyone have a photo of a 12AP4 or 9AP4 with a really bad ion burn?

Edit again:

The issue of focus is actually what has prevented fast neutron beam therapy from taking off. For certain tumors, especially tumors that are extremely hypoxic, neutron beams do more damage to the rogue DNA than proton beams, X-ray photons, etc. There's a problem with a neutron though: they are both relatively massive, and chargeless (well it may have a charge around 10^-22 e, so essentially chargeless). Because they are changeless, we can't focus them electro-statically or magnetically, so we must resort to collimating a "beam" from the neutrons produced. This is incredibly inefficient, and shaping the beam can be a bit of a challenge. The ion beam in a magnetic focus, magnetic deflection tube is analogous in some respects to a neutron beam: you'd better produce it with the direction you prefer, because you can't do anything to deflect/focus it later.

Kevin Kuehn

04-21-2017, 01:00 PM

Also note that WeekendHacker's analysis of ion deflection/ion burn size is incorrect.

If I'm not mistaken WH retracted that notion in his last response.

I retract my conclusion that ions must be materially deflected significantly by manetism. The vague circle pattern has a new and better explanation.

Tubejunke

05-12-2017, 12:48 PM

I've been thinking about buying the tuner and space command hardware off of you to upgrade mine to space command (it has the bezel microphone and chassis shelf space for space command but was not equipped) for a few years. It might finally be time for me to pull the trigger after the ETF.

OK, just let me know in a PM. I will make you a decent deal on the stuff. Like the set was; the parts are in immaculate condition. It's so hard to keep track of everyone. I am thinking that you may have some items worth making a trade on. I'm pretty much into nice vintage radios, meaning I'm getting few if any plain AA5s. 6 tube jobs with power transformers from the 30s and 40s are about the best of radios.

Also, I am into vintage test equipment, but I'm getting quite the pile of that stuff. My big wish is a black face Hickok 209A. Anything Hickok is worth consideration. I need a meter movement for a 209C which seems to be some rare bird.